Conventionally, X-rays for medical or industrial applications have been typically taken using films and screens. In this case, the use of resources and time becomes inefficient due to problems related to the development and storage of the taken films.
Hence, digital-type image sensors are currently widely used.
Such image sensors are classified into indirect conversion-type image sensors and direct conversion-type image sensors. Indirect conversion-type image sensors function such that X-rays are converted into visible light using a scintillator, after which the visible light is converted into an electrical signal. By comparison, direct conversion-type image sensors function such that X-rays are directly converted into an electrical signal using a photoconductive layer. Direct conversion-type image sensors are suitable for use in high-resolution systems because there is no need for an additional scintillator and the spreading of light does not occur.
The photoconductive layer used in the direct conversion-type image sensor is formed using a variety of materials. Recently, the photoconductive layer has been made from a semiconductor material having high atomic weight, such as CdTe, CdZnTe, PbO, PbI2, HgI2, GaAs, Se, TlBr, and BiI3. However, such a photoconductive layer exhibits poor adhesion to aluminum or copper (Cu), which may be used in a front electrode, undesirably causing the photoconductive layer to come loose.